Pour oil into 10-gallon pot and place pot on propane burner used for fish cooker. Heat oil to 375 degrees. Dry turkey and tie two cotton strings around carcass for ease in lifting. Carefully submerge turkey into hot oil and deep fry for 3 to 4 minutes per pound and until turkey floats to the top. Remove from oil and sprinkle with Cajun seasoning. In a saucepan, melt butter with garlic and cayenne. Brush turkey with mixture before serving.